1. Technical Field
The present invention relates to a package substrate and a fabricating method thereof, and more particularly, to a package substrate in which a metal post is made of a metal alloy and a heat-diffusion prevention film is formed on the metal post, and a fabricating method thereof.
2. Description of the Related Art
In general, a flip chip package has a structure that accesses a chip using a solder bump formed on a substrate. Since such a flip chip package aims at processing huge data at high speed, there is a trend of making a bump pitch smaller according to an increase in a data capacity to be processed including a current trend toward light, slim, short, and small semiconductors.
A change in the package caused by this trend causes a problem that bump reliability attenuates and thus a solution to this problem is urgently needed.
In order to improve reliability of bump access between the substrate and the chip, it has been suggested in the related art that solder, which is a bump material of the chip, is substituted with copper because mechanical strength is relatively higher and stable, and that a bump of the substrate is formed with a copper post.
In this case, solder is used as a medium for bonding the copper formed on the chip and the substrate, and in general, the solder is printed or plated for use on the copper poster formed on the substrate.
However, the related-art solder bump formed on the copper post has several problems in that a warpage phenomenon may occur between the substrate and the chip since the copper post easily oxidizes and its hardness is strong because of properties of copper, and accordingly, a short circuit phenomenon may occur on the copper post, if a crack appears on the copper post or warpage becomes more serious.
In order to solve these problems, the copper post is now substituted with various metal alloy materials. However, if the post is made of a metal alloy material, there is a problem in that a blister phenomenon occurs on a dry film between a metal seed layer and the dry film, and also, a problem that a plating layer is formed on an insulation layer on which a plating layer should not be formed or plating is not achieved on a pad on which a plating layer should be formed.
Also, if a reflow process is performed after the solder has been plated or printed on the copper post made of the metal alloy material, a boundary surface between the copper post and the solder disappears and thus the solder may flow to a top surface or a side surface of the copper post or the copper post may melt due to high temperature heat transmitted from the solder during the reflow process.